Abstract

Nutrient enrichment in the form of anthropogenic phosphorous and nitrogen inputs has occurred in lakes worldwide. In the absence of historical water chemistry data, the extent to which this disturbance has impacted lakes in the Erie/Ontario drift and lake plain and Western Allegheny Plateau ecoregions remains to be determined. The objective of this study was to develop a diatom calibration set through analysis of surface sediments and water chemistry from 30 lakes spanning a phosphorous and nitrogen gradient in the glaciated regions of northeast Ohio and northwest Pennsylvania with an additional lake in New York. No current training set exists for this unique geographic region. The relationship between diatom species and environmental variables was established using ordination techniques involving multiple regression and weighted-averaging methods. Canonical correspondence analysis (CCA) was used to determine environmental variables that have a strong influence on diatoms from the ecoregions studied. Total phosphorus, ammonia, and magnesium were the three most statistically significant variables determined through multivariate analyses, although maximum depth and nickel concentrations were also found to be important. At a total phosphorus inference model was developed from recent diatom fossil remains and contemporary water chemistry measurements. The ecological indicator values (optima and tolerances) of 40 abundant diatom species were defined using C2 computer software. The root mean squared error associated with prediction of the TP inference model was 17 ug/L, and the R2 linear coefficient of correlation between observed and diatom-inferred TP values was 0.77. The optima developed in this research match closely those constructed from calibration studies covering similar or longer TP gradients (12 ug/L-153 ug/L TP). A comparison with optima developed from other studies yields values much lower than those in this project and illustrates the need for regional calibration studies. This calibration set will be us